Can anyone recommend a nice beach in St. Maarten (Dutch side) where there are beach facilities that are good for kids? A friend of mine will be on a Disney cruise and would like to spend a day on a nice beach where the children can enjoy swimming and perhaps some water sports that may be available. How far is the beach from the dock and roughly would a taxi ride cost? Thank you.

Lots of choices in St Martin. One would be to simply go into town and go to the beach in Great Bay . Located downtown and behind all the stores. Not a bad place for dad to set up with the kids while mom shops for a while.
Another choice is Dawn Beach. Dutch side, about a 15 minute cab ride ( sorry don't remember price) . Family friendly beach, attracts locals, nearby condo dwellers and some cruise tourists. Restaurant, bar, facilities (at the restaurant) concession stand on the beach sells good food and drinks (cheap) and rents chairs and umbrellas. Offshore reef keeps the wave action down to just a small shore break.
There is another very family friendly beach over by the airport (name escapes me) . Kids have fun as planes fly close overhead.
Orient beach is of course the most popular. There is a clothing optional section at one end.
Do be prepared for the fact that even on the Dutch side, the occasional european tourist may go topless on just about any beach.